With a continuous development in cellular wireless mobile communication systems, there are more and more mobile users. Such a high speed development brings opportunities as well as pressures and challenges. Problems such as finite spectrum resources, sharply increasing volume of business, too large load of the base station, insufficient coverage area, etc., all need to be solved by researching new communication technologies.
The Long Term Evolution (LTE) system of the 3rd Generation Partnership Project (3GPP) Organization for Standardization supports two duplex ways, that is, Frequency Division Duplex (FDD) and Time Division Duplex (TDD). As shown in FIG. 1, FIG. 1 is a schematic diagram of an FDD wireless frame configuration in prior art. For a FDD system, each wireless frame has a length of 10 ms and includes 10 sub-frames each having a length of 1 ms. Particularly, the sub-frame is composed of two continuous time slots each having a length of 0.5 ms, that is, the kth sub-frame includes the time slots 2k and 2k+1, where k=0, 1, . . . 9. As shown in FIG. 2, FIG. 2 is a schematic diagram of a TDD wireless frame configuration in prior art. For a TDD system, each wireless frame of 10 ms is equally divided into two half frames each having a length of 5 ms. Particularly, each half frame includes 8 sub-frames each having a length of 0.5 ms and 3 special domains, that is, Downlink Pilot Time Slot (DwPTS), Guard Period (GP), and Uplink Pilot Time Slot (UpPTS), wherein the sum of the lengths of the 3 special domains is 1 ms. Each sub-frame is composed of two continuous time slots, that is, the kth sub-frame includes the time slots 2k and 2k+1, where k=0, 1, . . . 9. Downlink Transmission Time Interval (TTI) is defined in a sub-frame.
During the configuration of the TDD wireless frame, 7 kinds of uplink and downlink configurations are suppotive, as shown in table 1. In table 1, D represents the downlink sub-frame, U represents the uplink sub-frame, and S represents the special sub-frame including the above 3 special domains.
TABLE 1period oftransfor-Serial No. ofmationsub-frame No.configurationpoint01234567890 5 msDSUUUDSUUU1 5 msDSUUDDSUUD2 5 msDSUDDDSUDD310 msDSUUUDDDDD410 msDSUUDDDDDD510 msDSUDDDDDDD610 msDSUUUDSUUD
Particularly, the first n Orthogonal Frequency Division Multiplexing (OFDM) symbols of each downlink sub-frame can be used to transmit the downlink controlling information. The downlink controlling information includes Physical Downlink Control Channel (PDCCH) and other controlling information, where n equals to 0, 1, 2, 3, or 4. The rest OFDM symbols can be used to transmit Physical Downlink Shared Channel (PDSCH) or Enhanced PDCCH (EPDCCH). In the LTE system, PDCCH and EPDCCH carry Downlink Control Information (DCI) of the uplink or downlink channel resources, which are referred to as Downlink Grant (DL Grant) and Uplink Grant (UL Grant), respectively. In the LTE system, the DCI of different User Equipments (UE) are transmitted individually and respectively, and the DL Grant and the UL Grant are transmitted individually and respectively.
In an enhanced system of the LTE system, a greater operation bandwidth is obtained by combining a plurality of Component Carriers (CC). That is to say, Carrier Aggregation (CA) is used to constitute the downlink and the uplink of the communication system, thereby supporting a greater transmission rate. Here, the CC combined together not only can employ the same duplex way, i.e., all the cells are FDD cells or TDD cells, but also can use different duplex ways, i.e., the FDD cells and the TDD cells both exist. For a UE, the base station can be configured to operate in a plurality of cells, one of which is a primary cell (Pcell), and the others are referred to as secondary cells (Scell). In the above existing LTE CA system, both the HARQ re-transmission and an initial transmission for the same Transport Block (TB) are limited to the same CC. For the LTE CA system, Channel State Information (CSI) and Hybrid Automatic Repeat Request Acknowledgement (HARQ-ACK) transmitted based on Physical Uplink Control Channel (PUCCH) are performed only on Pcell. This limits the flexibility of the base station scheduling to some extent. In order to adapt to the requirements for evolution of the LTE system, it is needed to improve the effectiveness of HARQ transmission in a new scene. For example, in configuring cells having unlicensed bands for UE, the cells having the unlicensed bands can be generally configured as Scells of UE.
The unlicensed bands generally have been allocated for some other usages, such as the radar system and/or the Wireless Fidelity (WiFi) system of 802.11 series. The WiFi system of 802.11 series operates based on a mechanism of Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA). A Station (STA) must detect the wireless channel before transmitting signals, and the wireless channel can be occupied to transmit signals only if the wireless channel has been idle for a period of time. The STA can simultaneously use two mechanisms to determine the state of the wireless channel. On one hand, the STA can use a Carrier Sensing technology to detect the wireless channel actually. When other STA signals are detected or the detected signal power exceeds the set threshold, it is determined that the wireless channel is busy. At this time, a Clear Channel Assessment (CCA) report reported by a physical layer module of STA to its high level module indicates that the wireless channel is busy. On the other hand, the WiFi system of 802.11 series also introduces the virtual carrier sense technology, that is, Network Allocation Vector (NAV). A duration domain is included in each 802.11 frame, and the NAV value set according to the duration domain confirms that signals can not be transmitted on the wireless channel, wherein NAV is the time indicating the wireless channel needs to be reserved.
Further, a plurality of LTE systems can also be deployed simultaneously in the unlicensed bands. For example, the plurality of LTE systems may be affiliated to different operators, respectively. In order to keep the description simple, hereinafter, LTE apparatus is used to refer to base station and UE in general. In order to avoid interference with other LTE system apparatuses or other wireless system apparatuses, the LTE system apparatus first needs to detect the state of the channel before transmitting signals, the apparatus can occupy the channel only when the condition of occupying the channel is satisfied. Furthermore, the apparatus may occupy the channel for one or more sub-frames, and then the channel must be released, thereby giving opportunities for other apparatuses to occupy the channel.
By using the above method of vying for resources, a LTE apparatus has to release the channel resource after occupying the channel and transmiting data. When the number of apparatuses participating competition on the component carrier is relatively large, it may take the LTE apparatus a relatively long time to re-seize the channel and then make a HARQ re-transmission for data that were not unsuccessfully transmitted in the last time. This limits the effectiveness of HARQ transmission to some extent.